An engine may include a plurality of cylinders to provide a higher level of torque. During high torque demand conditions, intake manifold pressure may be high so that engine pumping losses may be reduced. However, at closed and part-open throttle conditions, engine efficiency may be reduced due to higher pumping losses and lower thermal efficiency. One way to reduce engine pumping losses while preserving engine torque at higher load conditions is to selectively activate and deactivate engine cylinders. Engine cylinders may be deactivated via holding intake and exhaust valves closed over an engine cycle without injecting fuel to the deactivated cylinders. Cylinders may be deactivated and reactivated in groups, but a large number of cylinder groups and firing patterns stored in controller memory may be necessary if cylinder activation and deactivation is based simply on switching on and off predetermined groups and patterns of engine cylinders. Therefore, it may be desirable to provide a way of selecting cylinders to be activated or deactivated without having to rely on predetermined cylinder groups or patterns.
The inventors herein have recognized the above-mentioned issues and have developed an engine control method, comprising: activating and deactivating a cylinder of an engine via a controller in response to an engine cylinder firing fraction and a remainder value, the remainder value based on the engine cylinder firing fraction.
By activating and deactivating cylinders of an engine in response to an engine cylinder firing fraction and a remainder value based on the cylinder firing fraction, it may be possible to provide the technical result of changing which cylinders of a cylinder are deactivated and not firing without having to store a large number of cylinder firing groups or patterns. In particular, an engine firing fraction may be a basis for calculations that have a remainder that varies between an upper value threshold and a lower value threshold. The remainder is updated for each most recent cylinder event (e.g., cylinder stroke or other cylinder related event), and an engine cylinder is activated or not activated based on a value provided by summing the engine cylinder firing fraction and the remainder. As the remainder moves back and forth between the upper value threshold and the lower value threshold, engine cylinders are activated or not activated. The engine cylinders are activated and combust air and fuel at a rate of the engine cylinder firing fraction.
The present description may provide several advantages. In particular, the approach may simplify cylinder deactivation by reducing complexity of skip activation cylinder control algorithms. Further, the approach provides for smooth transitions between operating an engine with different engine cylinder firing fractions. In addition, the approach may reduce controller memory usage by reducing engine cylinder groupings or patterns that form a basis for activating or deactivating engine cylinders.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.